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The present invention relates to a projection-type vehicular headlamp which also serves as an infrared light-emitting lamp used with a CCD camera having a sensitivity covering the near-infrared range. More particularly, the invention relates to a projection-type headlamp serving also as an infrared light-emitting lamp which is capable of forming simultaneously a visible light beam pattern having a cut line corresponding to the upper edge of a shade and a predetermined infrared light beam pattern by using the shade for reflecting visible light components while the infrared light component passes through the shade.
A conventional lamp of this general type is disclosed, for example, in Japanese Laid-Open Patent Application No. 2001-60403. As shown in FIGS. 14 and 15, in this projection-type headlamp serving also as an infrared light-emitting lamp an ellipsoidal reflector 3 and a projection lens 4 are disposed in a lamp chamber defined by a lamp body 1 and a front cover 2. A light source 5 is mounted at a first focal point f1 of the reflector 3, and a visible light shielding shade 6 is disposed near a second focal point f2 of the reflector 3. The light shielding shade 6 is made of a material which cuts visible light and passes infrared light, and thus, as shown in FIG. 16, the headlamp provides both a low-beam pattern Ps having a clear-cut line corresponding to an upper edge portion 6a of the light shielding shade 6 and a horizontally elongated ellipsoidal infrared light beam pattern Pa including the low beam pattern Ps.
This lamp functions as a low beam headlamp, for instance, when driving in an urban district or like, and also functions as an infrared light-emitting lamp used in an infrared xe2x80x9cnoctovisionxe2x80x9d system including an infrared light camera, display device, etc. That is, an infrared light irradiation area (the region illuminated by the beam pattern Pa) ahead of the vehicle is sensed by a CCD camera having a sensitivity including the near-infrared range and which is disposed in a forward portion on the vehicle, the output of the camera is processed by an image processing device, and the resulting image is displayed on a monitor screen in the vehicle. The driver thus can recognize pedestrians, lane markers, obstacles and the like on the monitor screen.
In particular, with regard to the function of the headlamp as an infrared light-emitting lamp, since the ellipsoidal infrared light beam pattern Pa overlaps the low beam pattern Ps, a sufficient infrared light intensity for operating the infrared light camera is obtained, and it is easy to recognize images displayed on the monitor.
In such conventional projection-type headlamp serving also as an infrared light-emitting lamp where, as shown in FIG. 14, the shade upper edge portion 6a and a light source 5 mounted on a reflector 3 are aligned on the optical axis L of a projection lens 4, a xe2x80x9chot zonexe2x80x9d PsH of the low beam pattern Ps is formed near the intersection of a horizontal line H and a vertical line V on a light distribution screen. Accordingly, although the forward visibility for the driver provided by this headlamp is excellent, some glare may be caused for drivers of oncoming vehicles in the adjacent lane, creating a safety problem.
As shown in FIG. 16, the problem of glare can be solved to some degree by aiming the headlamp in such a manner that the clear-cut line of the low beam pattern Ps is beneath the line H. However, such an approach also causes the hot zone of the infrared light beam pattern Pa to fall beneath the line H, thereby making the infrared light intensity at more remote distances insufficient for proper operation of the infrared camera and thus lowering the visibility at remote distances on the monitor screen.
The present invention has been made in consideration of the problems of the prior art described above, and it is hence an object of the invention to provide a projection-type headlamp serving also as an infrared light-emitting lamp which is capable of providing sufficient infrared light intensity ahead of the vehicle while preventing the visible light from causing glare to drivers of oncoming vehicles in the adjacent lane.
To achieve the object described above, a projection-type headlamp according to the invention serving also as an infrared light-emitting lamp is provided with an ellipsoidal reflector, a light source disposed at a first focal point of the reflector, a projection lens disposed ahead of the reflector, and a shade disposed near a second focal point of the reflector for shielding visible light while letting infrared light pass therethrough for thus forming simultaneously a visible light beam pattern having a cut line and an infrared light beam pattern, wherein the upper edge portion of the shade is positioned above the optical axis of the reflector.
The shade may be formed, for example, of an infrared light transmitting film disposed and fixed on a transparent glass plate at a specific position so as to form an infrared light-transmitting filter.
Since the upper edge portion of the shade is positioned above the optical axis of the reflector, the cut line and hot zone of the visible light beam pattern are located beneath the horizontal line H on the light distribution screen, and hence the visible light beam does not cause glare for vehicles in the adjacent lane. Moreover, since the hot zone of the infrared light beam pattern, which is not influenced by the shade, falls on the horizontal line H on the light distribution screen, the infrared light beam reaches a long distance, and the imaging performance of the infrared light noctovision camera is enhanced.
The upper edge portion of the shade may be formed in a convex shape, curved upward.
If the upper edge portion of the shade is straight in the lateral direction, the cut line of the visible light beam pattern on the light distribution screen is formed in a convex shape, curving downward, due to aberration effects of the lens, thereby reducing visibility. However, since, in accordance with the invention, the upper edge portion of the shade is formed in a convex shape curved upward, the cut line of the visible light beam pattern is substantially straight in the lateral direction, even taking into account the aberration effects of the projection lens, so that visibility is enhanced.
Also, a second shade for shielding visible light may be disposed above the shade.
In such a case, an infrared light CCD camera and a visible light CCD camera are installed as infrared noctovision cameras, and the images sensed by the two cameras are composed and displayed on the monitor. The visible light CCD camera has an automatic gain control function for adjusting the gain automatically to an optimum value so that the image output is not too high or too low by measuring the luminance of the viewing field ahead of the camera and adjusting the gain of the photodetector of the camera depending on the luminance or adjusting the aperture of an automatic iris of the camera (hereinafter referred to collectively as adjustment of the gain of the photodetector or the like of the camera). However, this automatic gain control function tends to reduce the gain of the photodetector or the like of the camera excessively due to the strong effects of light intensity (brightness) in the illuminated area near the vehicle where the solid angle is large. Therefore, the imaging performance is reduced in remote areas where the solid angle is small and the image of the remote area displayed on the monitor may be unclear. Accordingly, by partially shielding the portion of the visible light emitted to regions near the vehicle with the second shade, the visible light intensity in the illuminated area near the vehicle which could have adverse effects on the automatic gain control function is reduced, hence alleviating the excessively strong automatic gain control function of the visible light CCD camera and thereby improving the imaging performance in remote areas where the solid angle is small. On the other hand, since the infrared light is not shielded by the second shade and the infrared light intensity in the infrared light illuminated area is not reduced, the imaging performance of the infrared light CCD camera is not adversely affected. Therefore, when the images of the visible light CCD camera and infrared light noctovision CCD camera are composed, the monitor displays an image of the view ahead of the vehicle excellent in visibility in remote areas.
Still further in accordance with the invention, the visible light transmission efficiency may be adjusted to be larger closer to the edge portion side.
A specific structure for increasing the visible light transmission efficiency in the upper edge portion of the shade more at the edge portion side includes a structure whose thickness gradually changes in the upper edge portion of the shade, a structure of increasing density toward the edge of fine through-holes formed along the upper edge portion of the shade, and a structure of fine undulations continuously formed in the upper edge portion of the shade.
In the projection type headlamp of the invention, if the illumination contrast near the cut line of the visible light beam is excessive (i.e., the contrast of the cut line border is too sharp), the visibility tends to be reduced, but since the visible light transmission efficiency in the shade upper edge portion gradually changes in the vertical direction, the brightness contrast near the cut line of the visible light beam is lessened, that is, the sharpness of brightness contrast is reduced, so that the visibility is improved.
It is preferable that the visible light transmission efficiency at the lower edge portion of the second shade is designed to avoid reducing visibility due to sharp stripes of high contrast illuminated on the road surface, that is, it is preferred that the brightness of the illuminated pattern changes gradually, similarly to the visible light transmission efficiency in the upper edge portion of the shade forming the cut line.